The following description of the background of the invention is provided simply as an aid in understanding the invention and is not admitted to describe or constitute prior art to the invention.
In the central nervous system, neurons produce dopamine (D) and norepinephrine (NE) which act as neurotransmitters. The adrenal medulla produces both epinephrine (E) and NE while NE is liberated by postganglionic sympathetic nerves. Conversion of NE to E occurs mainly in the adrenal medulla. When catecholamines are released from sympathetic tissue, other than the adrenal medulla, the primary means of physiologic inactivation is the return of unaltered catecholamines by an active transport mechanism. The residual hormone may then be metabolized or excreted unchanged by the kidney.
Two enzymes are important for catecholamine metabolism; monoamine oxidase (MAO), which is responsible for oxidative deamination and catechol-O-methyltransferase (COMT), which is responsible of O-methylation. COMT is principally responsible for inactivating circulating catecholamines, whereas MAO is thought to play a role in disposing of excess catecholamine stores. The major end product for metabolism of E and NE is 3-methoxy-4-hydroxymandelic acid (VMA). The other urinary metabolites of the catecholamines are metanephrine and normetanephrine.
Tyrosine is the amino acid precursor of the catecholamines. The major catecholamine biosynthetic pathways are shown below.

Methods for purifying catecholamines in a sample utilizing boronic acid have been reported. See, e.g., Soga, T., et al., J. Chromatog. 1993, 620:175-81; and Eriksson, B., et al., J. Chromatog. 1992, 593:185-190. Various mass spectrometric techniques for measuring catecholamines in a sample have been reported. See, e.g., Smythe, G., et al., Clin. Chem. 1992, 38:486-92; Heki, N., et al., Nippon Naibunpi Gakkai Zasshi 1977, 53:785-96; Lemos-Amado, F., et al., Rapid Commun. Mass Spectrom. 2001, 15:2466-71; Chan, E., et al., J. Chromatog. B 2000, 749:179-189; Nimkar, S., et al., U.S. patent application Ser. No. 11/350,147 (filed Feb. 8, 2006); Chan, E., et al., Rapid Commun. Mass Spectrom. 2000, 14:1959-64; Tornkvist, A., et al., J Chromatog. B 2004, 801:323-9; Gu, Q., et al., Analytica Chimica Acta 2008, 609:192-200; Kushnir, M., et al., Clin. Chem. 2002, 48:323-31; and Carrera, V., et al., J Chromatog. B 2007, 847:88-94.